Reinforced roll and method of making same

ABSTRACT

A method of making an article adapted for use as a wear resistant working surface of a roll includes positioning hard elements in predetermined positions on a bottom surface of a mold. The hard elements comprise a first end and an opposed second end. The second end of each hard element rests on the bottom surface, partially filling a void space and defining an unoccupied volume in the mold. Inorganic particles are added to the mold to at least partially fill the unoccupied volume and provide a remainder space. The hard elements and the inorganic particles are heated to an infiltrating temperature and infiltrated with a matrix material. The matrix material is cooled and solidified and binds the hard elements and the inorganic particles in the article.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §120 as a divisionalapplication of co-pending U.S. patent application Ser. No. 12/502,277,filed on Jul. 14, 2009, which is incorporated herein in its entirety.

BACKGROUND OF THE TECHNOLOGY

1. Field of the Technology

The present disclosure is directed to rolls used for high pressurecomminution of granular materials such as, for example, minerals andores in high pressure grinding mills. More specifically, the disclosureis directed to articles adapted for use as wear resistant workingsurfaces of rolls and to methods of making the articles and rollsincluding the articles.

2. Description of the Background of the Technology

The comminution of granular materials such as, for example, minerals andores, is often carried out between rolls in a high pressure grindingmill. High pressure grinding mills typically utilize a pair of opposedcounter-rotating grinding rolls. The rotation axis of one of thegrinding rolls is fixed, and the rotation axis of the second roll isfloating. A hydraulic system connected to the floating roll controls theposition of the floating roll relative to the fixed roll, providingpressure between the rolls and an adjustable grinding force on materialpassing between the rolls. The rotational speed of the rolls is alsoadjustable to optimize the grinding conditions. By controlling the gapbetween the rolls, the speed of the rolls, and the applied force, theore or other materials passing between the rolls can be crushed in anefficient manner with relatively low energy input.

During high pressure grinding of granular materials, the material to beground is fed into the gap between the rolls. The gap is referred to asthe “nip”, and also may be referred to as the “roll gap”. The grindingof ore passing into the nip, for example, occurs by a mechanism ofinter-particle breakage caused by the very high pressures developedwithin the material stream as it passes between the counter-rotatingrolls. In addition, ore ground in this way exhibits cracks in the oregrains, which is beneficial to downstream processing of the ore.

As can be expected, the grinding operation exerts very high levels ofmechanical stress on the grinding rolls of high pressure grindingapparatuses, and the grinding rolls may quickly wear.

One known approach to improve the wear resistance of a roll surface isby welding layers of hard metallic material onto the surface. FIG. 1depicts a prior art grinding roll including a wear resistant weldedsurface layer. The welding process may be time consuming and expensive.

Another known approach to improve wear resistance of a grinding rollsurface is by providing hard regions that project from the workingsurface of the roll. FIG. 2 depicts two views of a prior art rollincluding welded hard regions projecting from the working surface of theroll. The top view in FIG. 2 is a magnified view of the roll surfaceshowing the individual projections and gaps between the projections. Thegaps trap fine grains of the material being ground, providing autogenouswear protection to the roll surface.

U.S. Pat. Nos. 5,203,513 and 7,497,396 disclose rolls adapted for use inhigh pressure grinding mills and that include hard projections with gapstherebetween. As with the prior art roll depicted in FIG. 2, the gapsbetween the hard projections trap fine particles of the material beingground, and the particles provide autogenous wear protection to the rollsurface. Also, friction between the trapped fine particles and thematerial being ground helps to draw the material to be ground into thenip. The method described in the '513 and '396 patents to fabricate therolls essentially involves welding the hard projections onto the rollsurface.

U.S. Pat. Nos. 6,086,003 and 5,755,033 also disclose rolls adapted foruse in high pressure grinding mills that include hard projections andgaps between the projections. The method described in the '003 and '033patents to fabricate the grinding rolls involves embedding hard bodieswithin a mass of metallic powder and consolidating the powder by hotisostatic pressing.

The methods for fabricating wear resistant high pressure rolls describedin the above-identified patents are costly and tedious. For example, theuse of a welding process to secure hard elements to a roll surfacelimits the range of materials from which the hard elements can befabricated. Hot isostatic pressing of a large roll requires the use ofexpensive equipment, and a grinding roll fabricated by hot isostaticpressing cannot be repaired easily in the field.

Accordingly, there is a need for articles and methods improving the wearresistance of the working surface of grinding rolls. It is desirablethat such articles and methods require relatively inexpensive equipment;allow a wide range of materials to be used as the projecting hardelements; permit tailoring of the base material used in the grindingroll; and permit easy repair of the roll surface in the field.

SUMMARY

According to one non-limiting aspect of the present disclosure, anarticle in the form of one of a plate, a sheet, a cylinder, and aportion of a cylinder, the article adapted for use as at least a portionof a wear resistant working surface of a roll, the article comprises ametal matrix composite comprising a plurality of inorganic particlesdispersed in a matrix material comprising at least one of a metal and ametal alloy The melting temperature of the inorganic particles isgreater than a melting temperature of the matrix material. A pluralityof hard elements is interspersed in the metal matrix composite. In anon-limiting embodiment a wear resistance of the metal matrix compositeis less than a wear resistance of the hard elements and the metal matrixcomposite may preferentially wear away when the article is in use,thereby providing or preserving a gap between each of the plurality ofhard elements at a working surface of the article.

In a non-limiting embodiment, a method of making an article adapted foruse as a wear resistant working surface of a roll includes positioning aplurality of hard elements in predetermined positions on a bottomsurface of a mold. Each of the hard elements comprises a first end andan opposed second end. A substantially equidistance exists between thefirst end and the opposed second end. The opposed second end of each ofthe hard elements rests on the bottom surface of the mold, so as topartially fill a void space of the mold and defines an unoccupied volumein the mold. Inorganic particles may be added to the mold to at leastpartially fill the unoccupied volume and provide a remainder spacebetween the inorganic particles and between the inorganic particles andthe hard elements. A non-limiting embodiment includes heating theplurality of hard elements and the inorganic particles to aninfiltrating temperature. The remainder space may be infiltrated with amatrix material comprising at least one of a molten metal and a moltenmetal alloy that has a melting temperature that is less than a meltingtemperature of the inorganic particles. The matrix material disposed inthe remainder space is to solidify the matrix material and bind the hardelements and the inorganic particles in the article.

A certain aspect of the disclosure includes a grinding roll for thecomminution of granular materials. In a non-limiting embodiment, agrinding roll may comprise a cylindrical core comprising an externalsurface, and at least one wear resistant article adapted for use as awear resistant working surface of the grinding roll, which is removablyattached to the external surface of the cylindrical core. The articlemay include a metal matrix composite comprising a plurality of inorganicparticles dispersed in a matrix material comprising at least one of ametal and a metal alloy, and a plurality of hard elements interspersedin the metal matrix composite. The wear resistance of the metal matrixcomposite may be less than a wear resistance of the hard elements, andthe metal matrix composite may preferentially wear away when thegrinding roll is in use, thereby providing or preserving a gap betweeneach of the plurality of hard elements at a surface of the article.

A method of one of manufacturing or maintaining a grinding roll mayinclude providing a cylindrical core comprising a external surface, andremovably attaching an embodiment of a wear resistant article disclosedherein to the external surface of the cylindrical core.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of articles and methods described herein maybe better understood by reference to the accompanying drawings in which:

FIG. 1 is a photograph of a prior art grinding roll having a weldedsurface;

FIG. 2 depicts photographs of a prior art grinding roll including weldedprojections comprising hard elements and gaps between the projections;

FIG. 3A is a schematic top view of a non-limiting embodiment of a wearresistant article according to the present disclosure;

FIG. 3B is a schematic cross-section of a non-limiting embodiment of awear resistant article according to the present disclosure, comprisingspaced-apart hard elements protruding from a metal matrix composite;

FIG. 3C is a schematic cross-section of a non-limiting embodiment of awear resistant article according to the present disclosure, comprisingspaced-apart hard elements with top surfaces that are substantiallyco-planar with a surface of a metal matrix composite;

FIG. 3D is a schematic cross-section of a non-limiting embodiment of awear resistant article according to the present disclosure, comprisinghard elements with top surfaces that are covered with a metal matrixcomposite;

FIG. 4 is a flow chart illustrating one non-limiting embodiment of amethod for manufacturing a wear resistant article according to thepresent disclosure adapted for use as a working surface of a roll;

FIG. 5A schematically illustrates positioning hard elements in a mold asa step in a non-limiting embodiment of a method of making a wearresistant article according to the present disclosure;

FIG. 5B schematically illustrates adding inorganic particles to a moldas a step in a non-limiting embodiment of a method of making a wearresistant article according to the present disclosure;

FIG. 5C schematically illustrates infiltrating a matrix material as astep in a non-limiting embodiment of a method of making a wear resistantarticle according to the present disclosure;

FIG. 6 is a schematic representation of top view of a non-limitingembodiment of a two piece vertical mold containing a non-limitingembodiment of a wear resistant article according the present disclosure;

FIG. 7 is a schematic representation of a non-limiting embodiment of agrinding roll according to the present disclosure, comprising a wearresistant article removably mounted to a surface of the roll; and

FIG. 8 is a photograph of a non-limiting embodiment of a wear resistantarticle according to the present disclosure.

The reader will appreciate the foregoing details, as well as others,upon considering the following detailed description of certainnon-limiting embodiments according to the present disclosure.

DETAILED DESCRIPTION OF CERTAIN NON-LIMITING EMBODIMENTS

In the present description of non-limiting embodiments, other than inthe operating examples or where otherwise indicated, all numbersexpressing quantities or characteristics are to be understood as beingmodified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, any numerical parameters set forth in thefollowing description are approximations that may vary depending on thedesired properties one seeks to obtain in the parts and methodsaccording to the present disclosure. At the very least, and not as anattempt to limit the application of the doctrine of equivalents to thescope of the claims, each numerical parameter described in the presentdescription should at least be construed in light of the number ofreported significant digits and by applying ordinary roundingtechniques.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein isincorporated herein only to the extent that the incorporated materialdoes not conflict with existing definitions, statements, or otherdisclosure material set forth in this disclosure. As such, and to theextent necessary, the disclosure as set forth herein supersedes anyconflicting material incorporated herein by reference. Any material, orportion thereof, that is said to be incorporated by reference herein,but which conflicts with existing definitions, statements, or otherdisclosure material set forth herein is only incorporated to the extentthat no conflict arises between that incorporated material and theexisting disclosure material.

According to an aspect of this disclosure, FIGS. 3A, 3B, 3C, and 3Ddepict schematic representations of non-limiting embodiments of anarticle 20, in the form of a plate, adapted for us as a wear resistantworking surface of a roll such as, but not limited to, a high pressuregrinding roll adapted for the comminution of granular materials. As usedherein, the “working surface” of a roll or other article is the surfaceof the article that contacts and exerts force on the material beingprocessed. FIG. 3A is a schematic top view of the article 20. FIGS.3B-3D are schematic cross-sections showing various aspects of an article20 taken through line a-a on FIG. 3A.

Referring to FIGS. 3A-3B, non-limiting embodiments of an article 20encompassed by an aspect of this disclosure comprise a metal matrixcomposite 21 comprising a plurality of inorganic particles 22 dispersedand embedded in a metallic (i.e., metal-containing) matrix material 23.In certain embodiments, the matrix material 23 comprises at least one ofa metal and a metal alloy. Also, in certain embodiments, the meltingtemperature of the inorganic particles 22 is greater than the meltingtemperature of the matrix material 23. While FIGS. 3A-3D suggest auniform distribution of the inorganic particles 22 dispersed in thematrix material 23, it is understood that FIGS. 3A-3D are non-limitingschematic representations useful in the understanding of embodimentsdisclosed herein and are not exhaustive of all embodiments according tothe present disclosure. For example, although the inorganic particles 22may be homogenously distributed in the matrix material 23, it is notnecessarily the case that the inorganic particles 22 are dispersed inthe regular fashion depicted in the schematic representations of FIGS.3A-3D.

A plurality of hard elements 24 are interspersed within the article 20.In an embodiment, the wear resistance of the metal matrix composite 21is less than the wear resistance of the hard elements 24. In such case,as shown in FIG. 3B, as the metal matrix composite 21 wears away duringuse, gaps 25 are created between each of the plurality of hard elements24 at the working surface 26 of the article 20. It is recognized,however, that the gaps 25 also can be partially or fully formed duringthe manufacture of the article 20.

In certain non-limiting embodiments, each of the hard elements maycomprise at least one of a high hardness metal, a high hardness metalalloy, a sintered cemented carbide, and a ceramic material. The terms“high hardness metal” and “high hardness metal alloy” are defined hereinas a wear resistant metal or metal alloy, respectively, having a bulkhardness equal to or greater than 40 HRC, as determined by the Rockwellhardness test, and measured according to the Rockwell C scale. Inanother non-limiting embodiment, the bulk hardness of the high hardnessmetal or high hardness metal alloy may be equal or greater than 45 HRC,as determined by the Rockwell hardness test. Examples of high hardnessmetal alloys include, but are not limited to, tool steels. Inembodiments wherein the hard elements 24 comprise a ceramic material,the ceramic material is a wear resistant ceramic material and may beselected from, but is not limited to, the group of ceramic materialincluding silicon nitride and aluminum oxide reinforced with siliconcarbide whiskers.

In another non-limiting embodiment, one or more of the hard elements 24may include a sintered cemented carbide. Non-limiting examples ofsintered cemented carbides that may be used for the hard elementsdisclosed herein are cemented carbides comprising particles of at leastone carbide of a Group IVB, a Group VB, and a Group VIB metal of thePeriodic Table dispersed in a continuous binder comprising at least oneof cobalt, a cobalt alloy, nickel, a nickel alloy, iron, and an ironalloy. Those skilled in the art are familiar with grades of cementedcarbide powders that, when processed, provide sintered cemented carbideshaving high strength and wear resistance, and the sintered cementedcarbides produced from such grades may be used to form certainnon-limiting embodiments of the hard elements 24 disclosed herein.Exemplary grades of cemented carbide powders useful in preparingsintered cemented carbide hard elements 24 that may be used innon-limiting embodiments of wear resistant articles according to thepresent disclosure include, but are not limited to, Grade AF63 and Grade231 available from ATI Firth Sterling, Madison, Ala.

In certain non-limiting embodiments according to the present disclosure,the hard elements are positioned and spaced apart in a predeterminedpattern. In certain non-limiting embodiments, the pattern of hardelements may be periodic and conform to a regular lattice-typestructure, or may be in irregular or aperiodic arrangements, which donot conform to a regular lattice structure. A non-limiting embodiment ofa pattern of a periodic arrangement of hard elements that may be used inan article according to the present disclosure is depicted in FIG. 3A.Other patterns may include repeating squares, triangles, and the like. Aspaced-apart arrangement of hard elements 24 in an article according tothe present disclosure also results in a corresponding arrangement ofgaps 25 between the hard elements 24.

For the efficient and economical operation of high pressure grindingmills, for example, the working surface of the rolls must be resistantto wear and abrasion and must efficiently draw the material to becomminuted into the nip. Referring again to FIGS. 3A and 3B, in certainnon-limiting embodiments of an article 20 according to the presentdisclosure adapted for use as a wear resistant working surface of agrinding roll, the gaps 25 between the hard elements 24 are regions inwhich fine particles (“fines”) of the material being ground are trapped.Friction between the fine particles trapped in the gaps 25 and thematerial to be ground helps to draw the material to be ground into thenip. The hard elements 24 and the trapped fines in the gaps 25, and anyexposed metal matrix composite 21 provide autogenous wear protection.Additional wear protection is provided by the metal matrix composite 21underlying the fines trapped in the gaps 25.

Any of the shape of the hard elements 24, the average distance betweenadjacent hard elements 24, i.e., the average gap distance, and theaverage size of the hard elements 24 of the article 20 can be varied toimpart different characteristics to the working surface of a grindingroll and thereby influence the comminution process. In addition, thegaps 25 between the hard elements 24 collect fine particles, i.e.,ground fines, which provide a protective surface over the matrixmaterial 23. The ground fines collected in the gaps 25 provide anexposed surface that is rougher than the any exposed surface of the hardelements 24, and thereby serve to provide areas of higher friction,which aids in drawing the material to be comminuted (ground) into thenip. If the gaps 25 are too small, the fines will tend not to accumulatein the gaps. If the gaps 25 are too large, a compact cake of the fineswill not form in the gaps 25. In the non-limiting embodiment depicted inFIG. 3A, the average gap distance is the average length of lines 25A and25B. In one non-limiting embodiment, the average gap distance may rangefrom 5 mm (0.2 inch) to 50 mm (2 inch). In another non-limitingembodiment, the average gap distance may range from 10 mm (0.4 inch) to40 mm (1.6 inch). It is recognized that these average gap distances aredirected to non-limiting embodiments of articles according to thepresent disclosure, and that other average gap distance values may bebeneficial for particular applications.

In one non-limiting exemplary embodiment of an article 20 according tothe present disclosure adapted for use as a wear resistant workingsurface of a roll, the pattern of the hard elements 24 may be similar tothe pattern schematically depicted in FIG. 3A, and the hard elements 24may be in the form of cylinders with substantially planar end surfaces.In certain non-limiting embodiments, an average diameter of the hardelements 24 may range from 10 mm (0.4 inch) to 40 mm (1.6 inch). Inother non-limiting embodiments, an average diameter of the hard elements24 may range from 15 mm (0.6 inch) to 35 mm (1.4 inch). It is recognizedthat these average hard element shapes, distributions, and diameters aredirected to non-limiting embodiments of articles according to thepresent disclosure, and that other shapes, distributions and/ordiameters may be beneficial for particular applications.

It will be understood that the hard elements 24 may be in a formdifferent from a cylinder and/or have ends that are non-planar, and thatthe hard elements 24 may not be of a uniform shape. For example, incertain embodiments the hard elements may be in the shape of a cube or acuboid, wherein the values for the average hard element diametersprovided above may be, for example, the average diagonal or average edgelength of a face of the cube or cuboid. A person skilled in the art willunderstand that hard elements 24 having other three-dimensional shapesare within the scope of embodiments disclosed herein, so long as aplurality of gaps 25 are provided between a plurality of the hardelements 24, either initially or, as discussed herein below, throughpreferential wear of the metal matrix composite when the article is inuse.

According to one non-limiting embodiment, the hard elements 24 comprise25% to 95% of a projected surface area of the surface of the article 20.In other non-limiting embodiments, the hard elements 24 comprise 40% to90%, or 50% to 80% of the projected surface area. It will be understood,however, that the hard elements may comprise any fraction of theprojected surface area of the hard elements suitable for the intendedapplication of the article 20. The term “projected surface area” isdefined herein as the two dimensional projection of the total surfacearea of the metal matrix composite 21 exposed at the working surface 26of the article 20 and the total surface area of the first ends 27 of thehard elements 24 (discussed below) exposed at the working surface 26.

Referring to FIG. 3B, a first end 27 of a hard element 24 is exposed onthe working surface 26 of the article 20. The first ends 27 of the hardelements 24 in FIG. 2B comprises a circular shape but, as discussedhereinabove, in other non-limiting embodiments the first ends 27 of thehard elements 24 may comprise a square shape, a rectangular shape, apolygonal shape, a complex curved shape, a shape having curved andlinear portions, or any other shape suitable for use in grinding theparticular granular material to be processed. In different non-limitingembodiments, the first ends 27 of the hard elements 24 may besubstantially planar, may be curved, may include planar and curvedregions, or may have a complex planar and/or non-planar geometry. Insome non-limiting embodiments, the first ends 27 of the hard elements 24may include points, ridges, and/or other features. It will be understoodthat the opposed second end 28 of a hard element 24 also may have any orall of the above possible physical characteristics of the first end 27.Generally, however, the ends 27 and 28 may be the same or different andmay have any characteristics suitable for the intended application ofthe article 20.

Referring to FIGS. 3B-3D, in certain non-limiting embodiments, the hardelements 24 of the article 20 may comprise a first end 27 and a opposedsecond end 28, wherein the first end 27 and opposed second end 28 are onopposite ends of a hard element 24. In certain embodiments, the firstend and the opposed second end 27,28 of each article are equidistant. Inthe article 20 illustrated in FIGS. 3C and 3D, the first ends 27 of thehard elements 24 are depicted as not projecting beyond the metal matrixcomposite 21 on the working surface 26 of the article 20 and, therefore,no gaps (such as gaps 25) are depicted on the working surface 26 betweenthe hard elements 24. FIGS. 3C and 3D depict possible non-limitingembodiments of article 20 immediately after manufacture, wherein thefirst ends 27 of the depicted hard elements 24 either are substantiallyco-planar with the surface of the metal matrix composite 21 at theworking surface 26 (FIG. 3C) or are embedded within (covered by) themetal matrix composite 21 (FIG. 3D). Because the wear resistance of thematrix composite 21 is less than the wear resistance a hard element 24,the metal matrix composite 21 will wear away more quickly than the hardelements 24 during use, which will tend to expose the first end 27 andthen the side surface(s) of the hard elements 24 in an incrementalfashion during use. For example, an article 20 manufactured in the formshown in FIG. 3D may transform to the form shown in FIG. 3C, and then tothe form shown in FIG. 3B as the metal matrix composite 21preferentially wears away and exposes the ends 27 and then progressivelymore of the side surface of the hard elements 24. As the metal matrixcomposite 21 wears away, the gaps 25 shown in FIG. 3B are created. Oncegaps 25 have been created, fines disposed in the gaps may aid ininhibiting wear of the underlying metal matrix composite 21 and/or aidin drawing material to be processed into the nip. It is recognized by aperson skilled in the art that a working surface may be located at theopposed second ends 28, because the article 20 in the form of a plate issubstantially symmetrical.

In a non-limiting embodiment, the first end 27 and the opposed secondend 28 of a hard element 24 are substantially planar and substantiallyparallel to each other. In one non-limiting embodiment, each of the hardelements 24 comprises a cylindrical shape and the first end 27 and theopposed second end 28 of a hard element 24 are substantially planar andsubstantially parallel to each other. In yet another non-limitingembodiment, each of the hard elements 24 comprises a cylindrical shapeand the first end 27 and the opposed second end 28 of each hard element24 exhibits a curvature. In still another non-limiting embodiment, eachof the hard elements 24 comprises a cylindrical shape and one of thefirst end 27 and the opposed second end 28 is substantially planar,while the other of the first end 27 and the opposed second end 28exhibits a curvature.

According to a non-limiting aspect of this disclosure, certainembodiments of the metal matrix composite 21 comprise inorganicparticles 22 having an average particle size ranging from 0.5 μm to 250μm. In other non-limiting embodiments, the inorganic particles 22 mayhave an average particle size ranging from 2 μm to 200 μm. In thevarious embodiments, the metal matrix composite 21 binds the hardelements 24 into the article 20.

In certain non-limiting embodiments according to the present disclosure,the inorganic particles 22 of the metal matrix composite 21 may compriseat least one of a metal powder and a metal alloy powder. In certainnon-limiting embodiments, the metal or metal alloy powder of the metalmatrix composite 21 comprises at least one of tungsten, a tungstenalloy, tantalum, a tantalum alloy, molybdenum, a molybdenum alloy,niobium, a niobium alloy, iron, an iron alloy, titanium, a titaniumalloy, nickel, a nickel alloy, cobalt, and a cobalt alloy.

In another non-limiting embodiment according to the present disclosure,the inorganic particles 22 of the metal matrix composite 21 may comprisehard particles. The term “hard particles” is defined herein as inorganicparticles exhibiting a hardness of at least 60 HRC, as measured by theRockwell hardness test using scale C. A non-limiting embodiment of themetal matrix composite 21 includes inorganic particles 22 comprising atleast one of a carbide, a boride, an oxide, a nitride, a silicide, asintered cemented carbide, a synthetic diamond, and a natural diamond.In yet another non-limiting embodiment, the inorganic particles 21comprise at least one of: a carbide of a metal selected from Groups IVB,VB, and VIB of the Periodic Table of the Elements; tungsten carbide; andcast tungsten carbide.

As noted above, the matrix material 23 of certain non-limitingembodiments comprises at least one of a metal and a metal alloy. In anon-limiting embodiment, the matrix material 23 includes at least one ofcopper, a copper alloy, aluminum, an aluminum alloy, iron, an ironalloy, nickel, a nickel alloy, cobalt, a cobalt alloy, titanium, atitanium alloy, a bronze alloy, and a brass alloy. In one non-limitingembodiment, the matrix material 23 is a bronze alloy consistingessentially of 78 weight percent copper, 10 weight percent nickel, 6weight percent manganese, 6 weight percent tin, and incidentalimpurities. In another non-limiting embodiment, the matrix materialconsists essentially of 53 weight percent copper, 24 weight percentmanganese, 15 weight percent nickel, 8 weight percent zinc, andincidental impurities. In non-limiting embodiments, the matrix material23 may include up to 10 weight percent of an element that will reducethe melting point of the matrix material, such as, but not limited to atleast one of boron, silicon, and chromium.

A non-limiting aspect of the article 20 according to the presentdisclosure includes providing the article 20 with at least onemachinable region 29. In certain non-limiting embodiments, a machinableregion 29 may comprise a region of metal or metal alloy joined to thearticle 20 by the metal matrix composite 21. Non-limiting embodiments ofa machinable region 29 may include a metal or a metal alloy comprisingat least one of iron, an iron alloy, nickel, a nickel alloy, cobalt, acobalt alloy, copper, a copper alloy, aluminum, an aluminum alloy,tantalum, and a tantalum alloy. In yet other non-limiting embodiments, amachinable region 29 of the article 20 may include particles of amachinable metal joined together by the matrix material 23 included inthe metal matrix composite 21. In certain non-limiting embodiments, theparticles of a machinable metal included in the machinable region 29 mayinclude at least one of iron, an iron alloy, nickel, a nickel alloy,cobalt, a cobalt alloy, copper, a copper alloy, aluminum, an aluminumalloy, tantalum, and a tantalum alloy. A machinable region 29 of thearticle 20 may be adapted for fixturing (i.e., connecting) the article20 to a peripheral surface of a roll (see FIG. 7) adapted to grind,pulverize, comminute, or otherwise process granular materials. Forexample, the roll may be a roll of a high pressure grinding mill adaptedfor comminuting granular materials. The machinable region 29 may bemachined to include features facilitating fixturing the article 20 to aperipheral surface of a roll. Machining the machinable region 29 mayinclude, but is not limited to, threading, drilling, and/or milling themachinable region 29.

One non-limiting embodiment of a method of making an article adapted foruse as a wear resistant working surface of a roll, such as, for example,article 20, is depicted in the flow diagram of FIG. 4, and thecross-sections of FIGS. 5A-5C. The cross-sections of FIGS. 5A-5Ccorrespond to sections taken at the line a-a in FIG. 2A. Referring toFIG. 2A, FIG. 4, and FIGS. 5A-5C, a non-limiting method 40 for making awear resistant article according to the present disclosure includespositioning 41 a plurality of hard elements 24 on a bottom surface 50 ofa mold cavity of a mold 51, so that an opposed second end 28 of each ofthe hard elements 24 rests on a bottom surface 50 of the mold cavity ofthe mold 51. The hard elements may or may not be positioned 41 in apredetermined pattern. In a non-limiting embodiment of the methodaccording to the present disclosure, the opposed second end 28 and thefirst end 27 of each hard element 24 are substantially planar and aresubstantially parallel to one another and to the bottom surface 50 ofthe mold cavity of the mold 51.

The mold 51 may be machined from graphite or any other suitablechemically inert material that can withstand the processing temperaturesof the methods disclosed herein without significantly warping orotherwise degrading. The mold 51 may be adapted to form a part that isin the shape of a plate, a sheet, a cylinder, a portion of a cylinder,or any other shape suitable to form all or a portion of a wear resistantworking surface of a roll when fixtured to the roll. A plate mold or asheet mold, for example, typically includes a mold cavity including asubstantially planar bottom surface and four upward extending sidewalls.

A mold cavity of a mold adapted to form a cylindrical part or a part inthe shape of a portion of a cylinder according to the present disclosuremay include a bottom surface that conforms to the curvature of all or aportion of the cylindrical peripheral surface of a roll. A non-limitingembodiment of a mold 51 that may be used to form an article 20 having acurved surface is schematically depicted in FIG. 6. Referring to FIG. 6and FIG. 3A, in a non-limiting embodiment, a curved mold 51 may comprisea vertical two-piece mold 51 having a first mold piece 52 including afirst curved surface 53, and a second mold piece 54 including a secondcurved surface 55. In a non-limiting embodiment, hard elements 24 may bepositioned on the first curved surface 53 of the first mold piece 52when the first mold piece 52 is horizontally oriented. The second moldpiece 54 may be mated with and secured to the first mold piece 52,holding the hard elements 24 in place in the mold cavity. The mold 51may then be moved to a vertical position, a top view of which isdepicted in FIG. 6. A plurality of inorganic particles 22 may be addedto the mold cavity of the mold 51, between the hard elements 24. Themold 51 may then be infiltrated with the matrix material 23 to form ametal matrix composite 21 with the inorganic particles 22.

Although the foregoing embodiment utilizes a mold 51 having curvedsurfaces in the mold cavity to make a curved article, it will beunderstood that non-limiting embodiments of an article according to thepresent disclosure also may be made in flat forms, such as plates orsheets. For example, in certain non-limiting embodiments, the metalmatrix composite 21 is ductile, and a wear resistant article 20 in theform of a plate or other flat form may be hot worked or otherwisesuitably processed to provide a curvature to the article 20 that matchesthe curvature of the peripheral surface of a roll to which the articleis to be attached.

The bottom surface 50 of a mold 51 used to form a wear resistant partaccording to the present disclosure may be further machined toaccommodate the contours or shapes of the opposed second ends 28 of thehard elements 24 that are disposed in the mold cavity of the mold 51 andform regions of the part made using the mold 51. Also, machiningcontours or shapes in the mold may aid in positioning the hard elements24. For example, the bottom surface 50 of a mold 51 may be machined toinclude contours such as, but not limited to, dimples to accommodatecorresponding curved opposed second ends 28 of hard elements 24.

Following is a description of additional details of certain non-limitingembodiments of methods of making wear resistant articles according tothe present disclosure, which will be better understood by reference toFIGS. 3A-D, 4, and 5A-C.

In one non-limiting embodiment of a method of making an article 20according to the present disclosure, comprises positioning 41 in themold cavity each of the hard elements 24, wherein the hard elements 24each comprise a first end 27 and an opposed second end 28 and thedistance between the ends 27 and 28 of each hard element 24 is the sameor approximately the same (i.e., the ends 27 and 28 are substantiallyequidistant). In certain non-limiting embodiments of a method accordingto the present disclosure, the opposed second end 28 of each of the hardelements 24 rests on the bottom surface 50 of the mold cavity of themold 51, so as to partially fill a void space in the mold cavity andthereby define an unoccupied volume 52 in the mold cavity, that is, thevolume in the mold cavity that is not occupied by the hard elements 24.

Another aspect of a non-limiting embodiment of a method according to thepresent disclosure comprises adding 42 inorganic particles 22 to themold cavity of the mold 30. The addition of inorganic particles 22 atleast partially fills the unoccupied volume 52 and provides a remainderspace (56 in the blown up section of FIG. 5B) in the mold cavity, thatis, the space between the inorganic particles 22 themselves and anyspace between the inorganic particles 22 and the hard elements 24 withinthe mold cavity of the mold 30.

In a non-limiting embodiment, the plurality of hard elements 24 and theinorganic particles 22 disposed in the mold cavity of the mold 51 areheated 43 to an infiltrating temperature (defined below). Heating 43 canbe achieved by heating the mold 51 containing the plurality of hardelements 24 and the inorganic particles 22 in a convection furnace, avacuum furnace, or an induction furnace, by another induction heatingtechnique, or by another suitable heating technique known to thosehaving ordinary skill in the art. In certain embodiments, the heatingcan be conducted in atmospheric air, in an inert gas, or under vacuum.

Following heating 43, the remainder space 56 is infiltrated 44 with amatrix material 23 comprising at least one of a molten metal and amolten metal alloy that has a melting temperature that is less than amelting temperature of the inorganic particles 22. Infiltrating 44 theremainder space 56 is accomplished at the infiltrating temperaturementioned hereinabove. Thus, it will be understood that the infiltratingtemperature is a temperature that is at least the melting temperature ofthe matrix material 23 that is infiltrated into the remainder space 56,but that is less than the melting temperature of the inorganic particles22. In certain non-limiting embodiments, an infiltration temperature mayrange from 700° C. (1292° F.) for low melting temperature metals andalloys such as, for example, aluminum and aluminum alloys, to 1300° C.(2372° F.) for higher melting temperature metals and alloys such as, forexample, copper, nickel, iron, cobalt, and alloys of any of thesemetals.

A further step of a non-limiting embodiment of a method according to thepresent disclosure includes cooling 45 the matrix material 23 disposedin the remainder space 56 to solidify the matrix material 23 and bindthe hard elements 24 and the inorganic particles 22 in the article 20.

In certain non-limiting embodiments, positioning 41 the hard elements 24comprises positioning 41 hard elements 24 that comprise at least one ofa high hardness metal, a high hardness metal alloy, a sintered cementedcarbide, and a ceramic. In yet another non-limiting embodiment, each ofthe hard elements 24 comprises a sintered carbide comprising particlesof at least one carbide of a Group IVB, a Group VB, or a Group VIB metalof the Periodic Table of the Elements dispersed in a continuous bindercomprising at least one of cobalt, a cobalt alloy, nickel, a nickelalloy, iron, and an iron alloy.

Adding 42 the inorganic particles 22 may include but is not limited toadding particles of a metal powder or a metal powder alloy. The metalpowder or metal alloy powder may comprise at least one of tungsten, atungsten alloy, tantalum, a tantalum alloy, molybdenum, a molybdenumalloy, niobium, a niobium alloy, iron, an iron alloy, titanium, atitanium alloy, nickel, a nickel alloy, cobalt, and a cobalt alloy.

In another non-limiting embodiment, adding 42 the inorganic particles 22may include, but are not limited to, adding hard particles. Hardparticles may include, but is not limited to, particles comprising atleast one of a carbide of a metal selected from Groups IVB, VB, and VIBof the Periodic Table of the Elements; tungsten carbide, and casttungsten carbide.

Infiltrating 44 with a matrix material 23 may include infiltrating intothe remainder space a metal or metal alloy that has a meltingtemperature that is less than the melting temperature of the inorganicparticles 22. The matrix material 23 may include, but is not limited to,at least one of copper, a copper alloy, aluminum, an aluminum alloy,iron, an iron alloy, nickel, a nickel alloy, cobalt, a cobalt alloy,titanium, a titanium alloy, a bronze alloy, and a brass alloy. In onenon-limiting embodiment, the matrix material is a bronze alloyconsisting essentially of 78 weight percent copper, 10 weight percentnickel, 6 weight percent manganese, 6 weight percent tin, and incidentalimpurities. In another non-limiting embodiment, the matrix material 23consists essentially of 53 weight percent copper, 24 weight percentmanganese, 15 weight percent nickel, 8 weight percent zinc, andincidental impurities.

Optionally, one of more machinable materials 29 may be positioned in themold cavity of the mold 51 at predetermined positions. Positioning oneor more machinable materials may include positioning one of more solidpieces comprising at least one of iron, iron alloy, nickel, nickelalloy, cobalt, cobalt alloy, copper, copper alloy, aluminum, aluminumalloy, tantalum, and tantalum alloy. In another non-limiting embodiment,positioning one or more machinable materials 29 comprises positioning aplurality of particles of at least one of a machinable metal and amachinable metal alloy in a region of the mold cavity, thereby creatinga second remainder space between the particles of the machinable metaland/or a metal alloy. After heating the mold and the materials in themold cavity to the infiltrating temperature, the matrix material isinfiltrated into the second remainder space and is then cooled to form asolid machinable region of the part 20. The particles of a machinablemetal and/or a machinable metal alloy may include, but are not limitedto, particles of iron, iron alloy, nickel, nickel alloy, cobalt, cobaltalloy, copper, copper alloy, aluminum, aluminum alloy, tantalum, andtantalum alloy.

Certain embodiments of a method of making an article adapted for use asat least a portion of a wear resistant working surface of a roll includecleaning the article after it is formed. In some embodiments, an excessof material may be machined from the article to form a finished articlethat is of a desired size and configuration. In other embodiments, afinished article is obtained after the cooling 45 step.

Advantages of the methods for producing the wear resistant articlesaccording to the present disclosure include, but are not limited to, thepossibility of using relatively inexpensive equipment to make thearticles, the possibility of using a wide range of materials to tailorthe characteristics of the articles, and the possibility ofincorporating one or more machinable regions on the article tofacilitate attachment (fixturing) and detachment of the wear resistantarticles from the peripheral surface of a roll.

Referring now to FIGS. 3A, 3B, and 7, an aspect of this disclosure isdirected to embodiments of a grinding roll 60 for the comminution ofgranular materials. In a non-limiting embodiment, a grinding roll 60comprises a cylindrical core 61, which has an external peripheralsurface 62. In certain non-limiting embodiments, the grinding roll 60may be comprised of a steel alloy or other material known to be suitablefor pressure rolling of granular material. At least one wear resistantarticle 63 according to the present disclosure that is adapted for useas at least a portion of a wear resistant working surface of thegrinding roll 60 is removably attached to the external peripheralsurface 62 of the grinding roll 60.

The wear resistant article 63 may comprise a metal matrix composite 21including a plurality of inorganic particles 22 dispersed in a matrixmaterial 23. The matrix material 23 may comprise a metal or metal alloyhaving a melting temperature that is less that the melting temperatureof the inorganic particles. A plurality of hard elements 24 may beinterspersed in and bonded together by the metal matrix composite 21 ofthe wear resistant article 63. In an embodiment, the wear resistance ofthe metal matrix composite 21 is less than a wear resistance of the hardelements 24, and the metal matrix composite 21 preferentially wears awaywhen the grinding roll 60 is in use, thereby providing or preservinggaps 25 between a plurality of the hard elements 24 at a surface 26 ofthe article 63.

The hard elements 24 of the wear resistant article 63 of the grindingroll 60 may include materials comprising, but not limited to, at leastone of a high hardness metal, a high hardness metal alloy, a sinteredcemented carbide, and a ceramic. In a non-limiting embodiment, the hardelements comprise a high hardness metal alloy that is a tool steel. Inanother non-limiting embodiment, each of the plurality of hard elements24 of the wear resistant article 63 comprises a sintered cementedcarbide.

In a non-limiting embodiment, the plurality of hard elements 24 of thewear resistant article 63 secured to grinding roll 60 comprise a firstend 27 and a opposed second end 28, wherein the first end 27 and opposedsecond end 28 are substantially planar and substantially parallel toeach other, and wherein for each hard element 24 a distance between thefirst end 27 and the opposed second end 28 is substantially the same.

The inorganic particles 22 of the wear resistant article 63 of thegrinding roll 60, in a non-limiting embodiment, comprise a metal powderor a metal alloy powder, which may be selected from, but is not limitedto, at least one of tungsten, a tungsten alloy, tantalum, a tantalumalloy, molybdenum, a molybdenum alloy, niobium, a niobium alloy, iron,an iron alloy, titanium, a titanium alloy, nickel, a nickel alloy,cobalt, and a cobalt alloy. In another non-limiting embodiment, theinorganic particles 22 comprise hard particles, which may include, butare not limited to, at least one of a carbide, a boride, an oxide, anitride, a silicide, a sintered cemented carbide, a synthetic diamond,and a natural diamond.

A grinding roll 60 may include a wear resistant article 63 comprising amatrix material 23 that includes, but is not limited to at least one ofcopper, a copper alloy, aluminum, an aluminum alloy, iron, an ironalloy, nickel, a nickel alloy, cobalt, a cobalt alloy, titanium, and atitanium alloy.

In certain non-limiting embodiments, the hard elements 24 of the wearresistant article 63 are spaced in a predetermined pattern in the metalmatrix composite 21. In other embodiments, not meant to be limiting, thehard elements 24 of the wear resistant article 63 comprise 25% to 95%,or 40% to 90%, or 50% to 80% of the projected surface area of thesurface 26 of the wear resistant article 63.

The wear resistant article 63 may further comprise at least onemachinable region 29 bonded to the article 63 by the metal matrixcomposite 21. The one or more machinable regions 29 may comprise atleast one of iron, an iron alloy, nickel, a nickel alloy, cobalt, acobalt alloy, copper, a copper alloy, aluminum, an aluminum alloy,tantalum, and a tantalum alloy. In a non-limiting embodiment, themachinable areas 29 of the wear resistant article 63 are removablyattached to the external peripheral surface 62 of the grinding roll 60by any means now or hereafter known to a person having skill in the art,including, but not limited to mechanical clamping, brazing, welding, andadhesives (including, but not limited to, epoxies). The provision of oneor more machinable regions 29 of the wear resistant article 63, and thepossibility of using many means to attach the machinable regions 29 (andthus the article 63) to the external peripheral surface 62 of a grindingroll 60, permits an article according to the present disclosure to beused with cylindrical grinding roll cores made from a variety ofmaterials.

A method of one of manufacturing and maintaining a grinding rollaccording to the present disclosure comprises providing a cylindricalcore 61 comprising an external peripheral surface 62, and attachingembodiments of the article 20 disclosed in FIGS. 2A and 2B andhereinabove to the surface 62. The article 20 may be attached to theexternal peripheral surface 62 of the grinding roll 60 by mechanicalclamping, brazing, welding, and/or adhesives (such as but not limited toepoxies), or by any suitable means known to a person skilled in the art.

EXAMPLE 1

Hard elements comprised of a sintered cemented carbide prepared fromGrade 231 cemented carbide powder, available from ATI Firth Sterling,Madison, Ala., were prepared using conventional powder metallurgytechniques, including the steps of powder compaction and hightemperature sintering. Grade 231 cemented carbide powder is a mixture of10 percent by weight of cobalt powder and 90 percent by weight oftungsten carbide powder. Powder compaction was performed at a pressureof 206.8 MPa (15 tons per square inch). Sintering was conducted at 1400°C. (2552° F.) in an over pressure furnace using argon gas at a pressureof 5.52 MPa (800 psi). The sintered cemented carbide prepared with Grade231 powder typically has a hardness of 87.5 HRA and a density of 14.5g/cm³. The hard elements had a form of substantially flat bottomedcylinders. A mold adapted to form articles having the shape of a squareplate was machined from graphite. The cylindrical cemented carbide partswere placed on the bottom of a mold cavity of the mold. The unoccupiedvolume in the mold, i.e., the space between the sintered cementedcarbide hard elements within the mold cavity, was filled with a blend of50 percent by weight of cast tungsten carbide powder and 50 percent byweight of nickel powder. A graphite funnel was placed on top of the moldassembly and bronze pellets were placed in the funnel. The bronzepellets had a composition of 78 weight percent copper, 10 weight percentnickel, 6 weight percent manganese, 6 weight percent tin, and incidentalimpurities. The entire assembly was disposed for 60 minutes in an airatmosphere in a preheated furnace maintained at a temperature of 1180°C. (2156° F.). The bronze melted and infiltrated the space between thecast tungsten carbide powder, the nickel powder, and the hard elements.The mold was allowed to cool, thereby allowing a metal matrix compositeto form comprising the cast tungsten carbide particles in a matrixmaterial comprising bronze and nickel. The cylindrical cemented carbideparts were embedded within the metal matrix composite. The wearresistant article was removed from the mold cavity and was cleaned, andexcess material was removed from the article by machining.

EXAMPLE 2

A photograph of the article fabricated in Example 1 is presented in FIG.8. The dark circular regions of the article are the hard elements. Thehard elements are surrounded by and bonded into the article by thelighter appearing metal matrix composite. The article may be hot workedor otherwise suitably processed to include a curvature matching thecurvature of a peripheral surface of a roll, and then may be secured tothe roll surface by welding or another suitable means.

It will be understood that the present description illustrates thoseaspects of the invention relevant to a clear understanding of theinvention. Certain aspects that would be apparent to those of ordinaryskill in the art and that, therefore, would not facilitate a betterunderstanding of the invention have not been presented in order tosimplify the present description. Although only a limited number ofembodiments of the present invention are necessarily described herein,one of ordinary skill in the art will, upon considering the foregoingdescription, recognize that many modifications and variations of theinvention may be employed. All such variations and modifications of theinvention are intended to be covered by the foregoing description andthe following claims.

1. A method of making an article adapted for use as a wear resistantworking surface of a roll, the method comprising: positioning aplurality of hard elements in predetermined positions on a bottomsurface of a mold; wherein each of the hard elements comprises a firstend and an opposed substantially equidistant second end, wherein thesecond end of each of the hard elements rests on the bottom surface ofthe mold to partially fill a void space of the mold and define anunoccupied volume in the mold; adding inorganic particles to the mold toat least partially fill the unoccupied volume and provide a remainderspace between the inorganic particles and between the inorganicparticles and the hard elements; heating the plurality of hard elementsand the inorganic particles to an infiltrating temperature; infiltratinginto the remainder space a molten matrix material comprising at leastone of a molten metal and a molten metal alloy, the matrix materialhaving a melting temperature that is less than a melting temperature ofthe inorganic particles; and cooling the matrix material disposed in theremainder space to solidify the matrix material and bind the hardelements and the inorganic particles in the article.
 2. The method ofclaim 1, wherein the mold comprises a mold adapted to form one of astrip and a plate.
 3. The method of claim 1, wherein the bottom surfaceof the mold comprises a curvature substantially equivalent to acurvature of the roll.
 4. The method of claim 1, wherein the first endand the opposed second end of each of the hard elements aresubstantially planar and substantially parallel to each other.
 5. Themethod of claim 4, wherein each of the plurality of hard elementscomprises a cylindrical shape.
 6. The method of claim 1, wherein thehard elements comprise at least one of a high hardness metal, a highhardness metal alloy, a sintered cemented carbide, and a ceramic.
 7. Themethod of claim 1, wherein each of the hard elements comprise a sinteredcemented carbide comprising: particles of at least one carbide of aGroup IVB, a Group VB, or a Group VIB metal of the Periodic Tabledispersed in a continuous binder comprising at least one of cobalt, acobalt alloy, nickel, a nickel alloy, iron, and an iron alloy.
 8. Themethod of claim 1, wherein the inorganic particles comprise at least oneof a metal powder and a metal alloy powder.
 9. The method of claim 8,wherein the inorganic particles comprise at least one of tungsten, atungsten alloy, tantalum, a tantalum alloy, molybdenum, a molybdenumalloy, niobium, a niobium alloy, iron, an iron alloy, titanium, atitanium alloy, nickel, a nickel alloy, cobalt, and a cobalt alloy. 10.The method of claim 1, wherein the inorganic particles comprise hardparticles.
 11. The method of claim 10, wherein the hard particlescomprise at least one of: a carbide of a metal selected from Groups IVB,VB, and VIB of the Periodic Table; tungsten carbide; and cast tungstencarbide.
 12. The method of claim 1, wherein the matrix materialcomprises at least one of copper, a copper alloy, aluminum, an aluminumalloy, iron, an iron alloy, nickel, a nickel alloy, cobalt, a cobaltalloy, titanium, a titanium alloy, a bronze alloy, and a brass alloy.13. The method of claim 12, wherein the matrix material is a bronzealloy consisting essentially of 78 weight percent copper, 10 weightpercent nickel, 6 weight percent tin, 6 weight percent manganese, andincidental impurities.
 14. The method of claim 12, where the matrixmaterial consists essentially of 53 weight percent copper, 24 weightpercent manganese, 15 weight percent nickel, 8 weight percent zinc, andincidental impurities.
 15. The method of claim 1, wherein positioning aplurality of hard elements on a bottom surface of mold in predeterminedpositions comprises positioning the hard elements in a predeterminedpattern.
 16. The method of claim 1, further comprising, prior to addinginorganic particles to the mold, positioning one or more machinablematerials in the mold at predetermined positions.
 17. The method ofclaim 16, wherein the one or more machinable materials comprise one ormore solid metal pieces comprising at least one of iron, an iron alloy,nickel, a nickel alloy, cobalt, a cobalt alloy, copper, a copper alloy,aluminum, an aluminum alloy, tantalum, and a tantalum alloy.
 18. Themethod of claim 1, further comprising adding a plurality of particles ofat least one of a machinable metal and a machinable metal alloy to atleast one void space in the mold, and thereby creating a secondremainder space between the at least one of a machinable metal and amachinable metal alloy particles, and further comprising infiltratingthe matrix material in the second remainder space.
 19. The method ofclaim 18, wherein the particles of the machinable metal and themachinable metal alloy comprise at least one of iron, an iron alloy,nickel, a nickel alloy, cobalt, a cobalt alloy, copper, a copper alloy,aluminum, an aluminum alloy, tantalum, and a tantalum alloy.
 20. Themethod of claim 1 further comprising cleaning the article.
 21. Themethod of claim 1 further comprising machining an excess material off ofthe article.